Nowadays, there is a tremendous interest in the development of portable, easy-to-use and low cost bioanalytical systems for the rapid diagnosis of genetic or infectious diseases. DNA hybridization biosensors have become one of such major diagnostic tools. Mostly, signal transduction of the hybridization event is based on optical, electrochemical, and microgravimetrical DNA methods. The electrochemical DNA biosensor holds, among all these, great promise due to a simple, rapid and inexpensive approach (1-4). Moreover, electrochemical DNA sensors could have the lower detection limit in the femtomolar or attomolar range, that usually is lower than the detection limit of general analytical techniques such as gel electrophoresis or membrane blots, which in addition are too slow and labour intensive.
Usually, electrochemical DNA hybridization biosensor is based on a one strand DNA (ssDNA) probe connected to a physical transducer whose properties are modified upon hybridization with the complementary DNA target to the probe. The goal of the sensor is to convert the DNA hybridization into an analytical signal measurable.
The DNA electrochemical sensors rely on the immobilization of a ssDNA or oligonucleotides onto the electrode surface to recognize through base pairing the complementary DNA strand (target) or oligonucleotides in a sample solution. The distribution, packing density and orientation of the attached probe may affect the performance of DNA biosensors.
Because of its importance, in literature there are several articles reviewing the design of DNA biosensors with aspect to transducer surface and probe immobilization towards sensitive hybridization detection. Thus, immobilization methods vary depending on the kind of transducer surface (gold, platinum, silver, indium tin oxide, etc.) and the application. Some of the most representative immobilization techniques are covalent attachment on a functionalized surface, adsorption on surface, embedding in sol-gel or polymeric matrix, affinity immobilization and self-assemble monolayer method (22).
Over the years, different forms of electrochemical DNA biosensors have been developed which transduce the DNA hybridization process using either a redox active molecule or a label free method which relies on the intrinsic redox-active properties of DNA base or a change of the electrical properties of the electrode interface upon hybridization, respectively (5-10, 23-34).
However, all known biosensors require the functionalization of their surface with specific ssDNA or oligonucleotides prior to the measurement. These biosensors are thus immersed into a solution containing a mixture with a ssDNA s and only the ssDNA target hybridizes onto the complementary ssDNA probe immobilized on the sensor.
Besides, such biosensors cannot be reused because they are modified by a specific oligonucleotide sequence.
Furthermore, all the DNA ligands as classical intercalators—like methylene blue—, groove binders and metal chelates are generally suffering from the impossibility of discriminating the double-stranded from the single-stranded DNAs, poor electrochemical performances in terms of reversibility, overpotential and/or stability.
One goal of the invention is therefore to avoid these drawbacks and to define an intercalator polymer that allows a better discrimination of dsDNA from ssDNA. Another goal of the invention is to define a new biosensor that does not need to be pre-modified with a specific DNA sequence probe. Another goal of the invention is to provide a biosensor that could be reused. Another goal of the invention is to define a method of detection of a DNA sequence that can discriminate better dsDNA from ssDNA.